China's mine safety production monitoring system has experienced the process of comprehensive monitoring from scratch, from simple to complex, from integrated machine to network, from secondary network to multi-level network. After more than ten years of application, the mine safety production monitoring system has played a significant role in China's coal mine safety production and modern management. However, since existing monitoring systems almost all use their own dedicated communication protocols, it is difficult to find two mutually compatible systems. At present, the compatibility of information transmission systems has become a limiting factor for the functions of the equipment monitoring system and the expansion of the system. Therefore, finding a way to solve the system compatibility problem is of great significance to promote the development of mine monitoring technology and the promotion and application of the system.
Current status of communication protocols used in mine safety production monitoring systems
A communication protocol is a set of rules used in a network to specify the format of information and how information is sent and received. Nodes in the network must follow the rules agreed by both parties to ensure the correct reception and transmission of data. At present, our self-developed KJ93 mine safety production monitoring system uses the RS-485 communication protocol, and its network structure is shown in Figure 1.
Application of CAN communication protocol
The mine safety production monitoring system is a system for monitoring and controlling the gas, ventilation, drainage and other conditions of coal mines and the working status of various electromechanical equipments, and using computer analysis to process the acquired data. Its characteristics can be summarized as follows: there are many kinds of monitoring and transmission data, the number of measuring points is large, the measuring points are widely distributed, and the use environment is extremely bad. Therefore, the principle that the mining product follows in selecting the bus protocol between systems or devices within the system is high reliability, high speed, and high real-time.
1. Feasibility of applying CAN communication protocol to mine safety production monitoring system
The CAN bus is a peer-to-peer inter-layer fieldbus network. The protocol is simpler than the RS-485 protocol, and has better real-time performance. Its information frame is short, and it will not affect other nodes to access the bus because of long-time transmission. Due to the priority arbitration technology, the high priority information can continue to be transmitted when a bus access conflict occurs, so it is more suitable for systems with high requirements for data transmission and real-time control in the mine.
CAN bus communication protocol and interface are simple, high transmission rate, with a variety of error detection methods, strong anti-interference, can meet the high reliability requirements of mine safety production monitoring system.
The biggest feature of the CAN protocol is that the traditional station address coding is abolished and the communication data block is encoded instead. The advantage of using this method is that the number of nodes in the network is theoretically unrestricted. This method of data block coding makes it easy to implement point-to-point communication. The data segment length is up to 8 bytes, which can meet the general requirements of control commands, working status and test data.
Due to the high communication speed, high reliability, convenient connection and other characteristics of CAN bus, it has effectively promoted the development of application development, which in turn prompted device manufacturers to continuously introduce new CAN bus products. At present, major semiconductor manufacturers are competing to launch CAN bus chips, such as the 82C200, SJA1000CAN communication controller and 82C250CAN bus transceiver introduced by Philips, the 82526 and 82527CAN communication controllers introduced by INTEL, and the 68HC05X4 and 68HC05X16 from MOTOROLA. The high-performance CAN bus products and technical data are available for availability and technical support, and the CAN bus can be applied to mining products.
In addition, the CAN communication protocol is also a bus protocol that fully satisfies the requirements of the "General Design Specification for Coal Monitoring Systems".
2. The overall composition of the mine safety production monitoring system
As shown in Figure 2, it is the network structure of mine safety production monitoring system using CAN communication protocol. CAN-bus and RS-485 have many similarities in electrical characteristics, network topology, and propagation media. At present, network topology based on CAN and RS-485 generally adopt terminal-matched bus-type structure, and there is no provision. Mechanical and material parameters of the bus cable. Therefore, replacing the RS-485 network with the CAN-bus network is very convenient and cost-effective. The original network layout does not need to be modified, and only the CAN node can be used to replace the RS-485 node. The main difference between this system and KJ93 mine safety production monitoring system is to replace the KJJ26 information transmission interface, monitoring system software and KJF20 workstation in the original system with CAN interface adapter, monitoring system software for CAN communication protocol and CAN based workstation. In addition, the monitoring host can also be connected to the server to access the LAN and the Internet for remote browsing and control.
In the mine safety production monitoring system, although the RS-485 communication protocol has been widely used, with the development of science and technology, the shortcomings and defects of the RS-485 communication protocol have become increasingly prominent, and the CAN communication protocol has its unique design idea and excellent The performance and high reliability have been paid more and more attention. The development of CAN international standards has further promoted its development and application. The use of CAN communication protocol in the mine safety production monitoring system improves the communication rate inside the system, which enhances the real-time performance of the system, reduces the error transmission rate, and better guarantees the security of the system.
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